This invention relates to positive displacement rotary pumps.
A positive displacement rotary pump typically includes a housing, an internal chamber in the housing, inlet and discharge ports in the housing intersecting the internal chamber, and a rotating group in the internal chamber defining a plurality of variable volume pump chambers which sweep in succession across and transfer fluid from the inlet port to the discharge port. The pump chambers traverse a sealing land on the housing between a downstream end of the inlet port and an upstream end of the discharge port and are sealed closed in the sealing land to prevent backflow from the discharge port to the inlet port. The pressure of the fluid trapped in the pump chambers in the sealing land is usually considerably below the high fluid pressure prevailing at the discharge port. Therefore, as succeeding ones of the pump chambers attain overlap with the upstream end of the discharge port, the fluid pressure therein increases rapidly to the high fluid pressure prevailing in the discharge port. The resulting regular pulses in the fluid in the discharge port and in the fluid system connected thereto constitute a potential source of pump noise having tonal character, i.e. noise that is concentrated at a discrete frequency and possibly whole number multiples of that frequency called harmonics. In positive displacement rotary vane pumps, it is known to suppress such noise by varying the angular separation between at least some of the vanes to alter the frequency content of the pulses. This approach is not universally applicable to all positive displacement rotary pumps, e.g. gerotor pumps and gear pumps. Consequently, manufacturers continue to seek improved positive displacement rotary pumps.
This invention is a new and improved positive displacement rotary pump including a housing having an internal chamber and inlet and discharge ports intersecting the internal chamber, a sealing land on the housing between a downstream end of the inlet port and an upstream end of the discharge port, and a rotating group in the internal chamber defining a plurality of pump chambers. The pump chambers sweep in succession across and transfer fluid from the inlet port to the discharge port and are sealed closed in the sealing land to prevent backflow. The housing has a stationary pre-charging passage which communicates with the discharge port and overlaps the sealing land. The rotating group includes a plurality of rotating pre-charging passages which communicate with respective ones of the pump chambers. As each rotating pre-charging passage attains overlap with the stationary pre-charging passage, the low pressure of the fluid trapped in the corresponding pump chamber sealed closed in the sealing land increases rapidly and induces a pulse in the fluid in the discharge port and in the fluid system connected to the discharge port. The angular separation between the rotating pre-charging passages is randomly unequal so that the intervals between the corresponding pulses is irregular. The irregularity of the intervals between the pulses suppresses tonal pump noise.